I'm not sure if it would be possible to add a touch-to-calculate the bpm functionlaty though..

I'm pretty sure a touch-to-calculate bpm is very possible to do, actually pretty easy. At least if I remember correctly how we could access the time the app had been running and we can perform arithmetics on it to calculate the time between screen taps, that would after 5 or so samples be able to provide an estimated bpm based on the average time between your taps.

Here is a quick Proof-Of-Concept that you can indeed calculate the Bpm by reading taps.
Feel free to use this in a Metronome app, just give a line of credit or something in the code or OP and I'm happy =P

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